The telecommunications industry is in the process of developing a new generation of flexible and affordable communications that includes high-speed access while also supporting broadband services. Many features of the third generation mobile telecommunications system have already been established, but many other features have yet to be perfected.
One of the systems within the third generation of mobile communications is the Universal Mobile Telecommunications System (UMTS) which delivers voice, data, multimedia, and wideband information to stationary as well as mobile customers. UMTS is designed to accommodate increased system capacity and data capability. Efficient use of the electromagnetic spectrum is vital in UMTS. It is known that spectrum efficiency can be attained using frequency division duplex (FDD) or using time division duplex (TDD) schemes. Space division duplex (SDD) is a third duplex transmission method used for wireless telecommunications.
As can be seen in FIG. 1 and FIG. 2, the UMTS architecture consists of user equipment 102 (UE), the UMTS Terrestrial Radio Access Network 104 (UTRAN), and the Core Network 126 (CN). The air interface between the UTRAN and the UE is called Uu, and the interface between the UTRAN and the Core Network is called Iu.
The UTRAN consists of a set of Radio Network Subsystems 128 (RNS), each of which has geographic coverage of a number of cells (C). The interface between the subsystems is called Iur.
Each Radio Network Subsystem 128 (RNS) includes a Radio Network Controller 112 (RNC) and at least one Node B 114, each Node B having geographic coverage of at least one cell. As can be seen from FIG. 6, the interface between an RNC 112 and a Node B 114 is called Iub, and the Iub is hard-wired rather than being an air interface. For any Node B 114 there is only one RNC 112. A Node B 114 is responsible for radio transmission and reception to and from the UE 102 (Node B antennas can typically be seen atop towers or preferably at less visible locations). The RNC 112 has overall control of the logical resources of each Node B 114 within the RNS 128, and the RNC 112 is also responsible for handover decisions which entail switching a call from one cell to another or between radio channels in the same cell. The one or more possible RNSs 128 interface with the core network 126, and in particular, with a serving GPRS support node SGSN 131 of the core network.
When a RNC (Radio Network Controller) has a RRC (Radio Resource Control) connection with a UE (User Equipment), it is known as the Serving Radio Network Controller (SRNC) for that UE. The SRNC is responsible for the users mobility within the UTRAN and is also the point of connection towards the CN (Core Network).
Typically, the interface between a user equipment (UE) and the UTRAN has been realized in the related art through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3). These layers are based on the lower three layers of an open system interconnection (OSI) model that is well known in communications systems.
For example, the physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the Medium Access Control (MAC) layer at L2 and the physical layer at L1, via a transport channel. The MAC layer is the lower of the two sublayers of the Data Link Layer. The transport channel is divided into a dedicated transport channel and a common transport channel depending on whether a channel is shared. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (receiver).
In this example of a typical system in the related art, the second layer L2 includes the MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer, and a packet data convergence protocol (PDCP) layer. The MAC layer maps various logical channels to various transport channels. The MAC layer also multiplexes logical channels by mapping several logical channels to one transport channel. The MAC layer is connected to an upper RLC layer via the logical channel. The logical channel can be divided into a control channel for transmitting control plane information, and a traffic channel for transmitting user plane information according to the type of information transmitted. The term “traffic” can sometimes be understood to cover control information, but in this present specification the term “traffic signal” will refer to a data signal in the user plane.
The MAC layer within L2 is divided into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, a MAC-hs sublayer and a MAC-e sublayer according to the type of transport channel being managed. The MAC-b sublayer manages a broadcast channel (BCH), which is a transport channel handling the broadcast of system information. The MAC-c/sh sublayer manages common transport channels such as an FACH (Forward Access Channel) or a DSCH (Downlink Shared Channel) that is shared by other terminals. The MAC-d sublayer handles the managing of a DCH (Dedicated Channel), namely, a dedicated transport channel for a specific terminal. The DCH is a portion of a Traffic Channel (forward or reverse) that carries a combination of user data, signaling, and power control information.
In order to support uplink and downlink high speed data transmissions, the MAC-hs sublayer manages an HS-DSCH (High Speed Downlink Shared Channel), namely, a transport channel for high speed downlink data transmission, and the MAC-e sublayer manages an E-DCH (Enhanced Dedicated Channel), namely, a transport channel for high speed uplink data transmissions.
In this example of a typical related art system, a radio resource control (RRC) layer located at the lowest portion of the third layer (L3) controls the parameters of the first and second layers with respect to the establishment, reconfiguration and release of radio bearers (RBs). The RRC layer also controls logical channels, transport channels and physical channels. Here, the RB refers to a logical path provided by the first and second layers of the radio protocol for data transmission between the terminal and the UTRAN. In general, the establishment of the RB refers to stipulating the characteristics of a protocol layer and a channel required for providing a specific data service, and setting their respective detailed parameters and operation methods.
A typical HSUPA (High Speed Uplink Packet Access) of the related art will now be briefly described. HSUPA is a system allowing a terminal or UE to transmit data to the UTRAN via the uplink at a high speed. The HSUPA employs an enhanced dedicated channel (E-DCH), instead of the related art dedicated channel (DCH), and also uses a HARQ (Hybrid Automatic Repeat Request) and AMC (Adaptive Modulation and Coding), required for high-speed transmissions, and a technique such as a Node B-controlled scheduling. For the HSUPA, the Node B transmits to the terminal downlink control information for controlling the E-DCH transmission of the terminal. The downlink control information includes response information (ACK/NACK) for the HARQ, channel quality information for the AMC, E-DCH transmission rate allocation information for the Node B-controlled scheduling, E-DCH transmission start time and transmission time interval allocation information, transport block size information, and the like. The terminal transmits uplink control information to the Node B. The uplink control information includes E-DCH transmission rate request information for Node B-controlled scheduling, UE buffer status information, UE power status information, and the like. The uplink and downlink control information for the HSUPA are transmitted via physical control channels such as an E-DPCCH (Enhanced Dedicated Physical Control Channel) in the uplink and E-HICH (HARQ acknowledgement Indication channel), E-RGCH (Relative Grant channel) and E-AGCH (Absolute Grant channel) in the downlink. For the HSUPA, a MAC-d flow is defined between the MAC-d and MAC-e. Here, a dedicated logical channel such as a DCCH (Dedicated Control Channel) or a DTCH (Dedicated Traffic Channel) is mapped to the MAC-d flow. The MAC-d flow is mapped to the transport channel E-DCH and the transport channel E-DCH is mapped to the physical channel E-DPDCH (Enhanced Dedicated Physical Data Channel). The dedicated logical channel can also be directly mapped to the transport channel DCH. In this case, the DCH is mapped to the physical channel DPDCH (Dedicated Physical Data Channel).
The present invention deals with a problem related to HSUPA and E-DCH, in the context of packet data traffic in Release 6 of 3GPP. A HARQ Failure Indication has been introduced in the document “3GPP TS 25.427, V6.5.0 (2005-12), UTRAN Iub/Iur interface user plane protocol for DCH Data Streams (Relaese 6)” which is incorporated by reference herein in its entirety. That failure indication is for improving OLPC (outer loop power control), by providing the number of retransmissions before a failure occurs.
The conditions that must prevail in order to send a failure indication are as follows. The serving Node B shall send a HARQ Failure Indication to the SRNC if a MAC-e protocol data unit (PDU) for a HARQ process has not yet been successfully decoded and the Retransmission Sequence Number (RSN) indicates the transmission of a new MAC-e PDU for the same HARQ process and the number of HARQ retransmissions that had already occurred was equal or higher than the lowest of the maximum HARQ retransmissions values for the UE's configured MAC-d flows. The serving Node B shall also send a HARQ Failure Indication to the SRNC if a MAC-e PDU for a HARQ process has not yet been successfully decoded and the maximum retransmissions for the MAC-d flow with the highest maximum HARQ retransmissions value valid for the UE connection have occurred, or should have occurred in case the HARQ related outband signalling (RSN) on the E-DPCCH could not be decoded.
There is a need to improve HARQ Failure Indications when a MAC-e reset is performed by a UE, which SRNC requests the UE to perform a flush/reset of all HARQ process for E-DCH, for improving OLPC. In case a UE is requested to perform the MAC-e reset, the UE resets all data in the buffer, i.e. the data for all HARQ processes (for E-DCH) not yet completed.
For example, FIG. 3 shows an Iub/Iur transmission when MAC-e reset is performed. As indicated in FIG. 3, a UE is configured to have one E-DCH MAC-d flow with maximum number of retransmission is set to 4. The Node B could not successfully decode the E-DCH data (MAC-e) with RSN=3 (actual number of the retransmission is 3) for a certain process and sends the UE NACK. However, before UE retransmits the data with RSN=3 (actual number of the retransmission is 4), UE performs the MAC-e reset and UE sends new data (MAC-e) with RSN=0 for the process. In the above example, at reception of new data in the Node B, the Node B does not send the HARQ Failure Indication since the two conditions noted above are not met. The SRNC executes OLPC calculation without data transmission at the processes 110 and 115. The SRNC has no information on how many retransmissions have occurred for the processes not yet completed before the MAC-e reset is performed by the UE. This degrades OLPC performance, especially when 10 ms transmission time interval (TTI) is used over air interface, as in FIG. 3.
It is assumed here that RNC will execute OLPC calculation every few hundred ms, such as every 200 ms. The transmission time interval TTI is the inter-arrival time of TBS (Transport Block Set), and is equal to the periodicity at which a Transport Block Set is transferred by the physical layer on the radio interface. It is always a multiple of the minimum interleaving period (e.g. 10 ms, the length of one Radio Frame RF). The MAC (Medium Access Control) delivers one Transport Block Set to the physical layer every TTI.
The serving Node B, which sends HARQ Failure Indications, has insufficient information to determine whether the termination of a HARQ process before it is completed is due to a MAC-e reset requested by SRNC or because of some other reason, such as NACK-ACK Error, especially, in SHO (soft handover) cases.
In addition, in case UE performs a MAC-e reset and a 2 ms TTI is used over the air interface and 10 ms is used over Iub/Iur, there is the possibility that one E-DCH DATA FRAME needs to include five 2 ms correct data frames and five HARQ Failure Indications, which require a total of ten sub frames, but it is not possible to include 10 sub frames in one E-DCH DATA FRAME according to the prior art, since the maximum number of sub frames in one E-DCH DATA FRAME is eight according to the prior art.